This invention pertains to nitrogen processing equipment typically used in the industry of well completion, well treatment, and enhancing the production of oil and gas from wells. More particularly, this invention pertains to flameless nitrogen processing units that use heat generated by internal combustion engines to vaporize liquid nitrogen by way of a common thermodynamic working fluid that is routed through a fluid commingling chamber of a recirculative heat exchange system.
Nitrogen processing units, often referred to within the industry as nitrogen converters, pump and convert low pressure liquid nitrogen into a high pressure liquid and/or gaseous nitrogen that is then used in a variety of operations and procedures used to induce and enhance the production of oil and gas from a wellbore. Nitrogen converters which do not use a direct flame to convert the liquid nitrogen are referred to as being "flameless" converters. Flameless type converters may be required or preferred in certain operating environments whether the well be located on land or offshore. Depending on the environment and the needed capacity, such units are truck body mounted, tractor trailer mounted, or skid mounted. Flameless type nitrogen converter units typically use waste heat from internal combustion engines that are needed to provide power to drive pumps used to transfer liquid nitrogen from storage tanks, or from engines that drive hydraulic systems that are used for operating related equipment, or from engines that are placed under a load in order to be a source of waste heat.
It is known within the art that converting low pressure liquid nitrogen into high pressure liquid/gaseous nitrogen can be achieved by readily using heat energy absorbed and transferred by an engine coolant, such as a liquid having anti-freezing characteristics. Such a liquid coolant is typically a mixture of ethylene glycol and water, or a functional equivalent thereof. The liquid coolant is circulated through cooling jackets of an engine usually by engine driven pumps. The then heated coolant is then routed to a commingling chamber of a predetermined volume, typically fabricated from a low carbon content steel or other suitable material used for forming low pressure vessels. The coolant still being at an elevated temperature, is then pumped out of the commingling chamber with the assistance of a separate auxiliary coolant pump to a heat exchanger referred to as a water bath vaporizer in which liquid nitrogen is being passed therethrough. Upon the liquid nitrogen receiving the heat energy previously stored in the heated engine coolant, the liquid nitrogen is vaporized, or more technically correct, converted as the nitrogen may be in either gas or liquid form, and is subsequently pumped and routed downhole or elsewhere for use in whatever operation is to be conducted at the job site. The now relatively cooler engine coolant may now be routed to a heat exchanger or a plurality of heat exchangers, that serve to cool transmission fluid for example, or hydraulic fluid, or it may be returned directly to the commingling chamber by the auxiliary coolant pump. A bypass valve may be installed wherein the coolant circulates only through the auxiliary pump, the nitrogen converter, and for example a transmission fluid heat exchanger and a hydraulic fluid heat exchanger, without being returned to the commingling chamber if so desired. Eventually, the coolant fluid is reintroduced to the commingling chamber wherein it is subsequently routed to the cooling radiator of the engine, or at some other point within the engine coolant loop. Regardless of where the coolant is reintroduced to the engine coolant loop, the coolant fluid is ultimately drawn into the engine whereupon the cycle is repeated.
The primary purpose of the commingling chamber is to provide a common juncture in which the coolant fluid can be shared by both the engine cooling loop and the nitrogen water bath vaporizer loop. The commingling chamber also provides a means to accommodate differing flow rates within these two flow loops. For instance, if the flow rate generated by the engine pump is different than the flow rate generated by the auxiliary converter pump, the two systems would suffer from fluid flow imbalance, and pump impeller cavitation and poor coolant circulation and possibly failures within one or both loops would result. A commingling chamber may also serve as an expansion chamber to allow for the thermal expansion of the coolant as it is subjected to heat. Alternatively, the commingling chamber can also serve as a juncture to a remote expansion chamber if so desired.
The above described system is somewhat simplified and in practice additional cooling loops and components are often used, but the overall scheme is exemplary of flameless type nitrogen converter units and particularly those available from the assignee of the present invention.
An exemplary prior art commingling chamber is shown in FIG. 1 of the drawings. Prior art commingling chamber 2 has a generally cylindrically-shaped vessel defined by wall 4 which is typically provided with an inlet port 6 for introducing heated coolant fluid from the engine, an outlet port 8 for directing commingled fluid to a nitrogen vaporizer, an inlet port 10 for reintroducing coolant fluid from a water bath nitrogen vaporizer (not shown in FIG. 1), and an outlet port 12 for redirecting commingled fluid to the engine. Top portion 14 of vessel 2 can be used as a coolant expansion chamber to allow for thermal expansion of the coolant if desired, and internal flow baffling 16 and 18 serve to enhance mixing of the fluid as it travels through chamber 2.
Because a coolant commingling chamber is an essential component in providing consistent and reliable operational characteristics of the engine and vaporizer coolant loops, there remains a long standing need to improve the design of such chambers without jeopardizing the ability of the commingling chamber to compensate for unequal flow rates between coolant loops sharing the same thermodynamic working fluid.
One reason for the need to improve the operating efficiencies of such commingling chambers is because there is an ever present need to reduce the overall size, weight, and footprint of equipment that is to be placed on offshore wells.
There is a similar long standing need to increase efficiencies for units placed on trucks and trailers as there are numerous size, gross weight, and load restrictions placed on such vehicles as well.
Furthermore, increasing efficiencies of such commingling chambers will allow for increased capacity of units without the need to bear associated costs attributable to an increase in engine size or nitrogen vaporizer size or other cost raising factors.